Electrosynthesis of Biomimetic Manganese-Calcium Oxides for Water Oxidation Catalysis-Atomic Structure and Functionality

Water‐oxidizing calcium–manganese oxides, which mimic the inorganic core of the biological catalyst, were synthesized and structurally characterized by X‐ray absorption spectroscopy at the manganese and calcium K edges. The amorphous, birnesite‐type oxides are obtained through a simple protocol that...

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Bibliographic Details
Published in:ChemSusChem 2016-02, Vol.9 (4), p.379-387
Main Authors: González-Flores, Diego, Zaharieva, Ivelina, Heidkamp, Jonathan, Chernev, Petko, Martínez-Moreno, Elías, Pasquini, Chiara, Mohammadi, Mohammad Reza, Klingan, Katharina, Gernet, Ulrich, Fischer, Anna, Dau, Holger
Format: Article
Language:English
Subjects:
Biomimetics
Calcium
Calcium - chemistry
Catalysis
Electrochemistry
manganese
Manganese - chemistry
Molecular Structure
Oxidation
Oxidation-Reduction
Spectrophotometry, Ultraviolet
Spectrum analysis
Water - chemistry
X-Ray Absorption Spectroscopy
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Summary:Water‐oxidizing calcium–manganese oxides, which mimic the inorganic core of the biological catalyst, were synthesized and structurally characterized by X‐ray absorption spectroscopy at the manganese and calcium K edges. The amorphous, birnesite‐type oxides are obtained through a simple protocol that involves electrodeposition followed by active‐site creation through annealing at moderate temperatures. Calcium ions are inessential, but tune the electrocatalytic properties. For increasing calcium/manganese molar ratios, both Tafel slopes and exchange current densities decrease gradually, resulting in optimal catalytic performance at calcium/manganese molar ratios of close to 10 %. Tracking UV/Vis absorption changes during electrochemical operation suggests that inactive oxides reach their highest, all‐MnIV oxidation state at comparably low electrode potentials. The ability to undergo redox transitions and the presence of a minor fraction of MnIII ions at catalytic potentials is identified as a prerequisite for catalytic activity. Catalyst Ca‐n do: Water‐oxidizing calcium–manganese oxides mimic the inorganic core of the biological catalyst. The oxides are electrodeposited and modified by active‐site creation through annealing at moderate temperatures. The ability to undergo redox transitions and the presence of a minority fraction of MnIII ions at catalytic potentials facilitates water‐oxidation catalysis.
ISSN:1864-5631
1864-564X
DOI:10.1002/cssc.201501399